For cellular networks applicable to immobile and mobile communications, W-CDMA has been standardized as a third generation cellular mobile communication scheme by 3GPP (3rd Generation Partnership Project), and services thereof have been sequentially provided. Further, HSDPA (High Speed Downlink Packet Access), which is a faster communication scheme, has also been standardized, and services thereof are about to be provided. Moreover, evolved universal terrestrial radio access (hereinafter, “EUTRA”) has been considered by 3GPP.
OFDM (Orthogonal Frequency Division Multiplexing) has been proposed as an EUTRA downlink. Additionally, DFT (Discrete Fourier Transform)-spread OFDM, which is a single-carrier communication scheme, has been proposed as an EUTRA uplink.
FIG. 21 schematically illustrates an EUTRA communication system. Wireless communication is performed among a base station BS and mobile stations MS1 to MS3. As shown in FIG. 21, an EUTRA downlink includes a downlink pilot channel, a downlink synchronization channel, a broadcast channel (BCH), a physical downlink shared channel, a physical downlink control channel (PDCCH), and a downlink shared channel (DL-SCH).
An EUTRA uplink includes an uplink pilot channel (UPiCH), a random access channel (RACH), an uplink shared channel (UL-SCH), and a physical uplink control channel (PUCCH). These are disclosed in, for example, Non-Patent Document 1.
FIG. 22 schematically illustrates, by hatched patterns, an example of random access channels (RACH), uplink shared channels (UL-SCH), and physical uplink control channels (PUCCH) being allocated to radio resources. Uplink pilot channels (UPiCH) are not shown.
Uplink pilot channels (UPiCH) are distributed and allocated in units of symbols or subcarriers within a region of an uplink shared channel (UL-SCH) or of a physical uplink control channel (PUCCH).
In FIG. 22, horizontal and vertical axes denote time and frequency, respectively. Each region included in the two-dimensional plane defined by time and frequency shown in FIG. 22 is a time-and-frequency region called a resource unit.
In the case of FIG. 22, each resource unit is defined by 1.25 MHz in the frequency direction and 1 ms (i.e., 1 TTI (Transmit Time Interval)) in the time direction. Thus, it is assumed in EUTRA that the minimum unit of RACH is one resource unit. Additionally, it is assumed that multiple random access channels (RACH) are included in 1 TTI, and that multiple mobile stations can simultaneously perform random access using different frequencies.
Hereinafter, a random access procedure (contention based random access procedure) is explained. A typical random access procedure is disclosed in, for example, Non-Patent Document 2.
FIG. 23 is a sequence chart schematically illustrating such a typical random access procedure. In a case of random access currently assumed in EUTRA, four massages are exchanged between a mobile station and a base station.
Firstly, the mobile station device transmits a random access preamble (message 1) using a random access channel (RACH).
Currently, it is assumed in EUTRA that the random access preamble includes a preamble ID that is a signal pattern indicative of information, and that the random access preamble ID is 6 bits of data. In other words, 2 to the 6th power (i.e., 64) preamble IDs are prepared. Additionally, it is assumed that a random ID is allocated to 5 bits of the 6 bits of the preamble ID, and random access reason, downlink path-loss/CQI (Channel Quality Indicator), or the like is allocated to the remaining 1 bit (see Non-Patent Document 2).
Upon receiving the random access preamble from the mobile station device, the base station device calculates a synchronization timing shift between the mobile station device and the base station device based on the random access preamble. Additionally, the base station device performs scheduling for transmitting an L2/L3 (Layer 2/Layer 3) message (message 3). Further, the base station device assigns C-RNTI (cell-radio network temporary identity) that is mobile-station identification information to a mobile station device requiring C-RNTI. Moreover, the base station device transmits a random access response including synchronization timing-shift information, scheduling information with respect to the message 3, the C-RNTI, and the preamble ID (message 2).
Then, the mobile station extracts the response from the base station which includes the transmitted preamble ID, retrieves scheduling information, and transmits an L2/L3 message using the scheduled radio resource (message 3).
Upon receiving the L2/L3 message from the mobile station, the base station transmits contention resolution to the mobile station to have the mobile station determine whether or not a contention among mobile stations is occurring (message 4).
One of problems of such a contention based random access procedure is that a contention of preambles occurs when different mobile stations transmit preambles by using the same random access channel (RACH) and by selecting the same preamble ID.
For this reason, a system for solving the problem on the random access contention has been considered. A random access procedure for solving the contention problem is called a non-contention based random access procedure in which the base station preliminarily assigns a preamble ID (which is called a dedicated preamble ID) to be transmitted by the mobile station. By using this system, a preamble contention among mobile station devices does not occur. Additionally, it is currently assumed that this system is used upon inter-cell handover or when uplink resynchronization is required for a mobile station to receive downlink data.
FIG. 24 is a sequence chart schematically illustrating a random access procedure (non-contention based random access procedure) using a dedicated preamble.
As shown in FIG. 24, firstly, the base station assigns a dedicated preamble ID to a mobile station, and transmits a message including the dedicated preamble (message 0).
Then, the mobile station performs random access using the dedicated preamble ID received by the dedicated preamble assignment (message 1).
Then, the base station receiving the dedicated preamble transmits, as a random access response (preamble response), a TA (Timing Advance) command (synchronization information) indicative of the synchronization timing shift to the mobile station (message 2).    [Non-Patent Document 1] R1-050850 “Physical Channel and Multiplexing in Evolved UTRA Uplink”, 3GPP TSG RAN WG1 Meeting #42 London, UK, Aug. 29-Sep. 2, 2005    [Non-Patent Document 2] 3GPP TS (Technical Specification) 36.300, V0.9.0 (2007-03), Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Overall Description Stage 2